Fluid pumps are widely used in different technical fields to pump fluids through a conveying system from one point to another point. Fluid pumps might also be used as rotary blood pumps used as ventricular assist devices (VADs) for long-term support comprising an impeller inside the blood pump pumping the blood from an inlet opening to an outlet opening. The main application remains as left ventricular assist device (LVAD) to support the systemic circulation. In the recent years so-called continuous flow devices have completely replaced pulsatile devices for the adult patient population. This is due to a number of reasons including high power density (increased hydraulic output with smaller devices), higher durability, and easier implantation including options for less invasive techniques. Blood pumps cannot be operated at a constant working point (layout point) representing a constant flow of blood over time since the blood flow in human beings strongly varies over time additionally being influenced by further contributing environmental circumstances. A major challenge during the development of a rotary blood pump as a long-term assist device is the bearing design for the impeller inside the blood pump for such operations. One approach is to completely levitate the rotor in the housing in order to avoid a mechanical contact between rotating and stationary parts. An example of a rotary blood pump is given in WO 2014/000753 A1.
During normal operation, the impeller has to be held in a certain position or position range to effectively convey blood. Therefore a bearing has to be applied to compensate forces, e.g. hydrodynamic forces, acting on the impeller during operation. In order to minimize the power consumption for the bearings and/or to simplify the bearing, e.g. requiring less bearing components, the forces acting on the impeller, especially the radially directed forces, during operation should be as small as possible. The principles valid for blood as a pumped fluid can also be applied on other fluids having similar properties.
It would be desirable to obtain a fluid pump, where at least the hydrodynamic radially directed forces acting on the impeller during operation at partial load are smaller compared to fluid pumps according to the state of the art.